The Humble Sources of 10 Major Rivers | Amusing Planet The Humble Sources of 10 Major Rivers Kaushik Saturday, April 18, 2015 1 comment Advertisement The source or headwaters of a river, defined as the furthest place in that river from its estuary or confluence with another river, is an elusive concept. On a colloquial basis, some define the source of a river at the drainage basin from which water runs year-around, such as a lake. Sometimes another river may flow into the lake, in which case the source of the other river is taken as the source of both rivers, as in the case of the river Nile. At other times, the confluence of two or more rivers where the river’s name is first used is taken as the source, as in the case of the river Danube. In many cases, it’s impossible to pinpoint the exact location from where a river begins, because a river has many sources. It often starts as a small stream but as it flows towards the sea or a lake or another river, the humble stream gathers water from numerous sources such as underground springs, rainwater, bogs, marshes and lakes and becomes a mighty river.

Let us see how some of the world’s biggest river began their journey. The Mississippi This is how the Mississippi River starts. Photo credit The Mississippi River is the chief river of the largest drainage system in North America flowing through 31 U.S. states and 2 Canadian provinces. It rises in northern Minnesota and flows southwards for 3,730 km to the Gulf of Mexico. The Mississippi ranks as the fourth longest and tenth largest river in the world. The primary source of the Mississippi River is Lake Itasca, located 450 m above sea level in Itasca State Park in Clearwater County, Minnesota. The name "Itasca" signifies the "true head" of the Mississippi River – the word is the combination of the last four letters of the Latin word for truth (veritas) and the first two letters of the Latin word for head (caput). However, the lake is in turn fed by a number of smaller streams, and by most modern definitions would be considered the actual source. A campaign was started in 1887 to promote another lake further upstream as the true source of the Mississippi.

After months surveying the lakes it was concluded that the lakes and streams further south of Lake Itasca were not the true source of the Mississippi because they were “too small.” The inflow of these streams into Lake Itasca were less dramatic than the lake's outflow. In 1891, Lake Itasca’s status was made official and a state park was created. The Nile One of the Nile’s sources in the Nyungwe Forest in Rwanda. Photo credit The Nile is the longest river in the world at 6,853 km. It’s located in northeastern Africa and its waters are shared by eleven countries. The Nile has two major tributaries, the White Nile and Blue Nile. The former is considered to be the headwaters and primary stream of the Nile itself, although the Blue Nile is the source of most of the water and silt. The source of the Nile is a matter of debate.

Sometimes Lake Victoria, from where the name "Nile" first appears, is considered to be the source of the river, but National Geographic and virtually every other geographic authority and atlas define the source of the Nile River not as Lake Victoria's outlet but instead use the source of the longest river flowing into the lake, the Kagera River. However, Kagera River itself has several tributaries and sources couldn’t agree on which is the longest tributary of the Kagera and hence the most distant source of the Nile itself. One of the tributaries, Ruvyironza, emerges in Bururi Province, in Burundi. Another tributary, the Nyabarongo, flows from Nyungwe Forest in Rwanda. One candidate for the most distant headwater of the Nile is the Rukarara River that starts in the Nyungwe Forest in western Rwanda. The Rukarara is a tributary of the Mwogo River, which in turn is a tributary of the Nyabarongo River. The Ganges The Bhagirathi River flowing out of the Gangotri Glacier.

Photo credit The Ganges, the most sacred river to Hindus, rises in the western Himalayas in the Indian state of Uttarakhand, and flows south and east through the Gangetic Plain of North India into Bangladesh, where it empties into the Bay of Bengal. It is the third largest river by discharge. The headwaters of the Ganges River begin high in the Himalayan Mountains where the Bhagirathi River flows out of the Gangotri Glacier in India's Uttarakhand state at a place called at Gaumukh (literally, “cow’s mouth”), at an elevation of 3,892 meters. The name “Ganges” begins at the confluence of the Bhagirathi and Alaknanda rivers at Devprayag. The Thames The Thames Head at Kemble. It remains dry most times of the year. Photo credit The River Thames flowing through London is the longest river in England and the second longest in the United Kingdom, after the River Severn. The source of the Thames is a spring called Thames Head that rises at a site in Gloucestershire, near the village of Kemble and the town of Cirencester. The place is marked by an ancient ash tree and a stone plaque.

If you are lucky you can see the spring coming out of the hillsides and a pool forming at the foot of the stone. But it isn’t always like that. Usually, no sign of water can be found at the source of the River Thames. The claim that Thames Head is the source of the River Thames is disputed. Some authorities hold that the true source of the Thames is at Seven Springs, Gloucestershire. Officially, however, Seven Springs is the source of the River Churn, a tributary of the Thames. The Danube The source of the Breg, the larger of two tributaries of Danube. Photo credit The Danube is Europe's second-longest river, located in Central and Eastern Europe. The river begins at the confluence of the two headstreams: Breg and Brigach near Donaueschingen, in the Black Forest area in Germany, almost at the border with Switzerland. However, the furthest source of the Danube is a karst spring located near the castle of Donaueschingen. From there, the stream flows underground below the so-called “Danube Temple”, that is situated on the Brigach river, to its current emergence point.

Officially, the Danube only comes into existence where the Danube stream connects with the confluence of the Brigach and Breg rivers. The Amazon River The most distant source of the might Amazon is this tiny glacial stream. Photo credit The Amazon River in South America is the largest river by discharge of water in the world with an average discharge that is greater than the next seven largest independent rivers combined. The Amazon basin is also the largest drainage basin in the world, and accounts for approximately one-fifth of the world's total river flow. The most distant source of the Amazon is a glacial stream located on a snowcapped 5,597 m peak called Nevado Mismi in the Peruvian Andes. The place is marked by a wooden cross. The waters from Nevado Mismi flow into the Quebradas Carhuasanta and Apacheta, which flow into the Río Apurímac which is a tributary of the Ucayali which later joins the Marañón to form the Amazon proper. The Rhine The flowing of the Rein da Tuma from Lake Toma.

Photo credit The Rhine river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps, then flows through the Rhineland and eventually empties into the North Sea in the Netherlands. It is the second longest river in Central and Western Europe. The headwaters of the Rhine is generally regarded as Lake Toma. Its outflow is called Rein da Tuma and after a few kilometers, it forms the Vorderrhein. The furthest headwater of both the Vorderrhein and the Rhine as a whole, however, is the Reno di Medel, rising about 7.5 km south of Lake Toma. Its spring and upper reaches are located West of the Lukmanier Pass in the municipality of Quinto in Ticino. The Volga The source of the Volga is marked by a church built here in the early 20th century. Photo credit The Volga is the longest river in Europe and also Europe’s largest river in terms of discharge and watershed. It flows through central Russia and into the Caspian Sea, and is widely viewed as the national river of Russia.

The river rises in the Valdai Hills 225 meters above sea level, northwest of Moscow and about 320 kilometers southeast of Saint Petersburg. There is a shrine at the location in the village of Volgoverkhovye. According to an ancient legend, the water at the source is considered healing and cleansing, and has been attracting pilgrims since the olden days. The Yellow River All of China's Sorrow arises from this puddle. Photo credit Called "the cradle of Chinese civilization", the Yellow River is the third-longest river in Asia and the sixth-longest in the world at the estimated length of 5,464 km. According to the China Exploration and Research Society, the source of the Yellow River is at the Bayan Har Mountains near the eastern edge of the Yushu Tibetan Autonomous Prefecture. The place is marked by a tablet. The Zambezi Photo credit The Zambezi is the fourth-longest river in Africa.

The 2,574-kilometer-long river rises in Zambia and flows through eastern Angola, along the eastern border of Namibia and the northern border of Botswana, then along the border between Zambia and Zimbabwe to Mozambique, where it crosses that country to empty into the Indian Ocean. The Zambezi's most noted feature is Victoria Falls. The river rises as a small bubbling stream in a jungle near Mwinilunga in the Kalene Hills, north-western Zambia, about 1,524 meters above sea level. The place is well marked and a popular tourist spot. Article based on this Imgur album Subscribe to our Newsletter and get articles like this delieverd straight to your inbox 1 comment: The Danube River - WorldAtlas.com Geography The Danube River Originating in the Black Forest of Germany, at 1,777 miles long the Danube is Europe's second longest river. The Danube as it runs through Budapest and past the Hungarian National Parliament buildings therein. 5.

Description Europe’s second longest river after the Volga, the Danube arises at the confluence of its headwaters, the Brigach and Breg Rivers, near the town of Donaueschingen in the Black Forest region of Germany. The river flows for a distance of around 2,857 kilometers, passing through 10 European countries along the way, and draining an area of 817,000 square kilometers, before finally draining into the Black Sea via the Danube Delta, which is shared between Romania and Ukraine. Romania shares 29% of the Danube’s river basin. Hungary, Serbia, and Austria each share approximately 10% of the river’s basin, while Germany, Bulgaria, Croatia, Slovakia, the Ukraine, and Moldova each share less than 10% of the Danube’s watershed. 4. Historical Role The Danube River has always played a prominent role in shaping the history of ancient Europe. Evidences of certain early human cultures, including the Danubian Neolithic culture and the Vučedol culture, have been found in the river basin.

Greek sailors exploited the river as early as the 7th Century BCE for trade purposes, while the Roman Empire used the river to define parts of the frontier boundaries of its kingdom. Fortresses and castles were built by the Romans on the river, and Roman fleets would patrol the river in efforts to defend the empire from its many tribal enemies living on the other side. The Ottoman Empire also used the Danube for defensive purposes in the later centuries to come. However, in the early 19th Century, the Queen of Hungary and Bohemia, Maria Theresa, recognized the potential of the Danube as a trade route, and thus started operating riverboats carrying cargo upon the river. In the following years, several treaties were signed and conventions were held to determine and discuss the sharing of the Danube’s waters. As a result of years and years of such negotiations, currently only those countries bordering the river are allowed exclusive rights to access the water resources of the Danube. 3. Modern Significance Today, the Danube River is like a lifeline for much of Europe, providing drinking water to over 20 million people and housing more than 83 million people in its watershed.

The ten countries sharing the waters of the Danube use the river for navigation, hydroelectric power generation, fishing, and the irrigation of farmlands alike. Water needed for industrial and domestic uses are also extracted from this river. Izmayil in Ukraine, Ruse in Bulgaria, Budapest in Hungary, and Vienna in Austria are some of the important port cities based along the river. A number of navigation channels have been constructed along the river, including the Danube–Black Sea Canal and the Main–Danube Canal, facilitating the transport of people and goods along and across the river. The Ðerdap (Djerdap) High Dam and the Iron Gate power station, situated between Serbia and Romania, is the largest hydroelectric power-generating project on the Danube. The Danube River Basin is also riddled with significant tourist spots. As a result, leisure cruises are commonplace on the river, and the presence of globally famous cities and cultures, as well as an abundance of natural wealth, draw millions of tourists into the countries sharing the river basin. 2.

Habitat and Biodiversity The extensive Danube River Basin supports a wide variety of natural habitats, like the Black Forest of Germany, the Alpine ecosystem of Austria, the puszta plains of Hungary, the wetlands of the Danube Delta, and the Danube islands of Bulgaria. More than 100 fish species, including 5 species of sturgeon, inhabit the waters of the Danube River. The river basin also supports a large variety of avian fauna, including such rare bird species as the Black stork, White pelican, and White-tailed eagle. The Danube River basin is also a part of the Worldwide Fund for Wildlife's “Global 200” list of ecoregions. 1. Environmental Threats and Territorial Disputes The Danube River, like most major rivers of the world, has been overfished and overpolluted. The lethal combination of pollutant release into the Danube’s waters, illegal and irresponsible fishing, and extensive damming of the river’s waters has resulted in a severe decline in the water quality of the Danube.

There are 28 dams on the Danube, ranging from its source to the mouth of the river delta, which block the natural flow of its waters and disrupt the natural order of sediment transfer from upstream to downstream, consequently facilitating heavy erosion in the river delta as well. These dams also act as a barrier to the natural migration of fish species of the river. Today, the level of damage to the river is so high that several kinds of sturgeon, fish species whose eggs are famous for caviar and have survived for 200 million years on Earth, are presently "endangered" in the region. This page was last modified on June 6, 2016. On WorldAtlas.com Source & Course of the Danube | Danube River Source & Course of the Danube Source & Course of the Danube Where to find the source of the Danube River? In 15 BC Tiberius Claudius Nero (42 BC-37 AD), Roman Emperor (14-37 AD), led the campaign through the Upper Rhine Valley to the Lake Constance to force the Celts into subjugation.

When the conquering Romans advanced further to the north, they discovered the headwaters of the Danube River in the modern-day Germany. The headwaters of the Danube River are situated in the Swabian Jura in a so called Karst-Area, a unique landscape that results from the weathering of bedrock types that are soluble in water. These bedrock sediments are primarily limestone. Rainwater slowly infiltrates cracks in the limestone, dissolving the rock and enlarging the underlain openings and underlain caves. Millennia of water flowing through these landforms creates unique and sensitive ecosystems. The Karst-Area is characterized by a subsurface network, and a lack of surface streams. The subsurface network has developed under stable conditions, consistent temperature and humidity, over thousands of years. During the summer, when water levels of the Danube are quite low, in the Upper Basin, the river is known to sink into a series of underground channels at various points of its course, what is known as Donauversickerung. Curiously, the word translates from German as the 'disappearance of Danube'.

Obviously, this area is not navigable by boat, but where river cruises terminate at Kelhaim, curious explorers who want to follow the river all the way to the source can plan further excursions to these enticing Karst Areas. They will find that the stream does not seep through the soil, but smoothly flows through a sequence of underground craters. This sounds almost like a fable. The stream reappears in the area further south of Aachtopf, north into Constance Lake, where it flows into the Rhine, thus linking the Black Sea with the Northern Sea. It is fascinating knowing that the two rivers come together, and that is how the nature carves out its own course. The question where to find the genuine source of the Danube River has kept scholars busy for centuries. Is it in Donaueschingen, in St. Georgen or in Furtwangen? The fact is that all three towns are situated in the Black Forest, in the district of Schwarzwald-Baar, in Baden-Württemberg, one of the 16 federal states, in the southwestern Germany. Today this question has definitely been settled.

The Danube River begins at the confluence of the two headstreams: Breg and Brigach near Donaueschingen, in the Black Forest. It is almost at the border with Switzerland, and an area that is a known habitat and spices protection area. In 1538 the Cosmographer Sebastian Münster (1488-1552), one of the most eminent German humanists and all-round scholars, marked the source of the Danube River with a quadrangle on a map and inscribed it with "fons danubii" (Lat.: the source of the Danube). Furthermore, he described the Donaubach as "Danuvius" and explained how Donaubach and Brigach come to form the Danube River. Therefore the extent of the Danube River started at the confluence of these rivers in this time period. In 1544 the Geographer and Mathematician Heinricht Loriti "Glarean" (1488-1563) also confirmed that the Danube River is formed by the rivers Brigach and Breg.

Danube River Facts Danube River Facts Danube River Facts The Danube River is the second longest river in Europe, flowing 1,785 miles from Germany to Ukraine into the Black Sea. The Danube River is a major water source in Europe and is Eastern Europe's chief source. The Danube River originates in the Germany's Black Forest where the Breg and Brigach Rivers converge. The Danube River's watershed is 315,445 square miles in size and the average discharge is 6,600 cubic meters per second. The Danube River got its name from the Proto-Indo-European word 'dānu' which has been used for naming several old European rivers. Interesting Danube River Facts: Some of the earliest human cultures lived in the vicinity of the Danube River - in its basin. The Danube is the second longest river in Europe after the River Volga. The Danube River flows through or along 10 countries including Germany, Austria, Slovakia, Hungary, Serbia, Croatia, Bulgaria, Moldova, Ukraine, and Romania. The Danube River flows through several countries' capital cities including Vienna, Belgrade, Budapest, and Bratislava.

The Danube passes through many other European cities including Ulm, Ingolstadt, Regensburg, Linz, Gyor, Danaujvaros, Vukovar, Novi Sad, Zemun, Pancevo, Drobeta Turnu-Severin, and Vidin. The Danube River's tributaries include Iller, Lech, Altmuhi, Naab, Regen, Isar, Inn, Enns, Morova, Raba, Vah, Hron, Ipel, Sio, Drava, Vuka, Tisza, Sava, Timis, Great Morava, Caras, Jiu, Iskar, Olt, Osam, Arges, lalomita, Siret, and Prut. Approximately 20 million people rely of the Danube River for their drinking water. The Danube River was once extremely important for fisherman but this has declined since the Middle Ages. Some regions are still very active but there are also a variety of endangered species in the Danube River such as sturgeon species.

Tourism along the Danube River is diverse with natural places of interest including the Wachau Valley, Hungary's Gemenc, Germany's Nationalpark Donau-Auen, Croatia's, Kopački rit, Romania and Serbia's Iron Gate, Romania's Danube Delta, and Bulgaria's Srebarna Nature Reserve. The Danube River is often used for leisure boating and travel cruises, with as many as 70 cruise ships between Vienna and Budapest alone. There is a bike trail along the Danube River called the Danube Bike Trail. It is divided into four sections along the river including Donaueschingen-Passau, Passau-Vienna, Vienna-Budapest, and Budapest-Black Sea. It begins and ends where the Danube River begins and ends. The Danube River is a graveyard for many German ships. During World War II the Germans sunk their ships to avoid allowing the Soviets to gain control of them. The Danube River is considered to be one of the most important shipping routes in Europe. Its size will accommodate the largest shipping vessels when necessary. It is estimated that there are more than 5000 species of animals, birds, and plants in the Danube's delta.

Approximately one-third of the Danube River passes through Hungary's borders. In 1991 the Danube River was designated a UNESCO Heritage Site. There have been more than 700 dams constructed on the Danube River's tributaries in various European countries. The Danube River has been featured in songs, novels, legends, and movies. Related Links: Danube River | Geology Page Danube River tweet Map of the Danube River The Danube is a river in Central and Eastern Europe, the European Union’s longest and the continent’s second longest (after the Volga). Classified as an international waterway, it originates in the town of Donaueschingen—which is in the Black Forest of Germany—at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for 2,872 km (1,785 mi), passing through four capital cities before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.

Once a long-standing frontier of the Roman Empire, the river passes through or touches the borders of ten countries: Romania (29.0% of basin area), Hungary (11.6%), Serbia (10.2%), Austria (10.0%), Germany (7.0%), Bulgaria (5.9%), Slovakia (5.9%), Croatia (4.4%), Ukraine (3.8%), and Moldova (1.6%). Its drainage basin extends into nine more. Names and etymology The name Dānuvius is presumably a loan from a Scythian language, or possibly Gaulish. It is one of a number of river names derived from a Proto-Indo-European language word *dānu, apparently a term for “river”, but possibly also of a primeval cosmic river, and of a Vedic river goddess (see Danu), perhaps from a root *dā “to flow/swift, rapid, violent, undisciplined.” Other river names with the same etymology include Don, Donets, Dnieper and Dniestr.

Dniepr (pre-Slavic Danapir by Gothic historian Jordanes) and Dniestr, from Danapris and Danastius, are presumed from Scythian Iranian *Dānu apara “river afar” and *Dānu nazdya- “river near”, respectively. The Danube was known in Latin as Danubius, Danuvius, Ister, in Ancient Greek as Ἴστρος (Istros). The Dacian/Thracian name was Donaris/Donaris (Τάναις in Greek, upper Danube) and Istros (lower Danube). Its Thraco-Phrygian name was Matoas, “the bringer of luck”. The Ancient Greek Istros was a borrowing from Thracian/Dacian meaning “strong, swift”, akin to Sanskrit iṣiras “swift”. Since the Norman conquest of England, the English language has used the Latin-derived word Danube. Geology Although the headwaters of the Danube are relatively small today, geologically, the Danube is much older than the Rhine, with which its catchment area competes in today’s southern Germany.

This has a few interesting geological complications. Since the Rhine is the only river rising in the Alps mountains which flows north towards the North Sea, an invisible line beginning at Piz Lunghin divides large parts of southern Germany, which is sometimes referred to as the European Watershed. Before the last ice age in the Pleistocene, the Rhine started at the southwestern tip of the Black Forest, while the waters from the Alps that today feed the Rhine were carried east by the so-called Urdonau (original Danube). Parts of this ancient river’s bed, which was much larger than today’s Danube, can still be seen in (now waterless) canyons in today’s landscape of the Swabian Alb. After the Upper Rhine valley had been eroded, most waters from the Alps changed their direction and began feeding the Rhine. Today’s upper Danube is but a meek reflection of the ancient one.

The Iron Gate, on the Serbian-Romanian border (Iron Gates natural park and Đerdap national park) Since the Swabian Alb is largely shaped of porous limestone, and since the Rhine’s level is much lower than the Danube’s, today subsurface rivers carry much water from the Danube to the Rhine. On many days in the summer, when the Danube carries little water, it completely oozes away noisily into these underground channels at two locations in the Swabian Alp, which are referred to as the Donauversickerung (Danube Sink). Most of this water resurfaces only 12 km south at the Aachtopf, Germany’s wellspring with the highest flow, an average of 8500 liters per second, north of Lake Constance—thus feeding the Rhine. The European Water Divide applies only for those waters that pass beyond this point, and only during the days of the year when the Danube carries enough water to survive the sink holes in the Donauversickerung.

Since such large volumes of underground water erode much of the surrounding limestone, it is estimated that the Danube upper course will one day disappear entirely in favor of the Rhine, an event called stream capturing. The hydrological parameters of Danube are regularly monitored in Croatia at Batina, Dalj, Vukovar and Ilok. Note : The above story is based on materials provided by Wikipedia Share this: Danube River | river, Europe | Britannica.com Danube River Alternative Titles: Donau, Duna, Dunaj, Dunărea, Dunav, Dunay Related Topics István, Count Széchenyi Danube River, German Donau, Slovak Dunaj, Hungarian Duna, Serbo-Croatian and Bulgarian Dunav, Romanian Dunărea, Ukrainian Dunay , river , the second longest in Europe after the Volga . It rises in the Black Forest mountains of western Germany and flows for some 1,770 miles (2,850 km) to its mouth on the Black Sea . Along its course it passes through 10 countries: Germany, Austria , Slovakia , Hungary , Croatia , Serbia , Bulgaria , Romania , Moldova , and Ukraine .

The Danube River basin and its drainage network. Encyclopædia Britannica, Inc. Boats along the Danube River, Belgrade, Serbia. Jon Arnold/SuperStock The Danube River links the countries of the Balkan Peninsula to each other and to the rest of … Encyclopædia Britannica, Inc. The Danube played a vital role in the settlement and political evolution of central and southeastern Europe. Its banks, lined with castles and fortresses, formed the boundary between great empires, and its waters served as a vital commercial highway between nations. The river’s majesty has long been celebrated in music. The famous waltz An der schönen, blauen Donau (1867; The Blue Danube ), by Johann Strauss the Younger , became the symbol of imperial Vienna. In the 21st century the river has continued its role as an important trade artery. It has been harnessed for hydroelectric power, particularly along the upper courses, and the cities along its banks—including the national capitals of Vienna (Austria), Budapest (Hungary), and Belgrade (Serbia)—have depended upon it for their economic growth.

Central Budapest, looking north along the Danube River, with the Parliament Building on the east … Jean S. Buldain/Berg & Assoc. Physical features Physiography The Danube’s vast drainage of some 315,000 square miles (817,000 square km) includes a variety of natural conditions that affect the origins and the regimes of its watercourses. They favour the formation of a branching, dense, deepwater river network that includes some 300 tributaries, more than 30 of which are navigable. The river basin expands unevenly along its length. It covers about 18,000 square miles (47,000 square km) at the Inn confluence , 81,000 square miles (210,000 square km) after joining with the Drava , and 228,000 square miles (590,000 square km) below the confluences of its most affluent tributaries, the Sava and the Tisza . In the lower course the basin’s rate of growth decreases.

More than half of the entire Danube basin is drained by its right-bank tributaries, which collect their waters from the Alps and other mountain areas and contribute up to two-thirds of the total river runoff or outfall. The confluence of the Sava (foreground) and Danube rivers from the Kalemegdan fortress, Belgrade, … Jean S. Buldain/Berg & Assoc. Opium Wars The river carries considerable quantities of solid particles, nearly all of which consist of quartz grains. The constant shift of deposits in different parts of the riverbed forms shoals. In the stretches between Bratislava and Komárno and in the Sulina Channel, draglines are constantly at work to maintain the depth needed for navigation. The damming of the river has also changed the way in which sediments are transported and deposited. Water impounded by reservoirs generally loses its silt load, and the water flowing out of the dam—which is relatively silt-free—erodes banks farther downstream. The temperature of the river waters depends on the climate of the various parts of the basin. In the upper course, where the summer waters derive from the Alpine snow and glaciers, the water temperature is low.

In the middle and lower reaches, summer temperatures vary between 71 and 75 °F (22 and 24 °C), while winter temperatures near the banks and on the surface drop below freezing. Upstream from Linz the Danube never freezes entirely, because the current is turbulent. The middle and lower courses, however, become icebound during severe winters. Between December and March, periods of ice drift combine with the spring thaw, causing floating ice blocks to accumulate at the river islands, jamming the river’s course, and often creating major floods. The natural regime of river runoff changes constantly as a result of the introduction of stream-regulating equipment, including dams and dikes. The mineral content of the river is greater during the winter than the summer. The content of organic matter is relatively low, but pollution increases as the waters flow past industrial areas. The river’s chemistry also changes as city sewerage and agricultural runoff find their way into the river.

The economy The Danube is of great economic importance to the 10 countries that border it—Ukraine, Moldova, Romania, Serbia, Croatia, Hungary, Bulgaria, Slovakia, Austria, and Germany—all of which variously use the river for freight transport, the generation of hydroelectricity, industrial and residential water supplies, irrigation, and fishing . The movement of freight is the most important economic use of the Danube. Among the major ports are such cities as Izmayil , Ukraine; Galați and Brăila , Romania; Ruse , Bulgaria; Belgrade, Serbia; Budapest, Hungary; Bratislava, Slovakia; Vienna, Austria; and Regensburg, Germany. Since World War II , navigation has been improved by dredging and by the construction of a series of canals, and river traffic has increased considerably. The most important canals—all elements in a continentwide scheme of connecting waterways—include the Danube–Black Sea Canal , which runs from Cernovadă, Romania, to the Black Sea and provides a more direct and easily navigable link, and the Main–Danube Canal , completed in 1992 to link the Danube to the Rhine and thus to the North Sea .

Boats along the Danube River, Belgrade, Serbia. Jon Arnold/SuperStock The Danube has been tapped for power, mainly in its upper course. The process, however, has spread downstream. One of the largest hydroelectric projects—the Ðerdap (Djerdap) High Dam and the Iron Gate power station—was built jointly by Yugoslavia and Romania. Not only does the project produce hydroelectricity, but it also makes navigable what was once one of the most difficult stretches on the river. Industrial use of Danube waters is made at Vienna, Budapest, Belgrade, and Ruse. The main irrigated areas are along the river in Slovakia, Hungary, Serbia, and Bulgaria. The river has nearly become unfit for irrigation as well as for drinking water, however, because of the tremendous increase in pollutants; pollution has also diminished the once-rich fishing grounds, although some of the fish have moved to side lakes and swamps. History During the 7th century bce, Greek sailors reached the lower Danube and sailed upstream, conducting a brisk trade. They were familiar with the whole of the river’s lower course and named it the Ister.

The Danube later served as the northern boundary of the vast Roman Empire and was called the Danuvius. A Roman fleet patrolled its waters, and the strongholds along its shores were the centres of settlements, among them Vindobona (later Vienna), Aquincum (later Budapest), Singidunum (later Belgrade), and Sexantaprista (later Ruse). During the Middle Ages the old fortresses continued to play an important role, and new castles such as Werfenstein, built by Charlemagne in the 9th century, were erected. When the Ottoman Empire spread from southeastern to central Europe in the 15th century, the Turks relied upon the string of fortresses along the Danube for defense. The Habsburg dynasty recognized the navigational potential of the Danube. Maria Theresa , queen of Hungary and Bohemia from 1740 to 1780, founded a department to oversee river navigation, and in 1830 a riverboat made a first trip from Vienna to Budapest, possibly for trading purposes. That trip marked the end of the river’s importance as a line of defense and the beginning of its use as a channel of trade.

Maria Theresa, portrait by W.H. Mote, 1861. The Print Collector/Heritage-Images Regulated navigation on the Danube has been the subject of a number of international agreements. In 1616 an Austro-Turkish treaty was signed in Belgrade under which the Austrians were granted the right to navigate the middle and lower Danube. In 1774, under the Treaty of Küçük Kaynarca , Russia was allowed to use the lower Danube. The Anglo-Austrian and the Russo-Austrian conventions of 1838 and 1840, respectively, promoted free navigation along the entire river, a principle that was more precisely formulated in the Treaty of Paris of 1856, which also set up the first Danubian Commission with the aim of supervising the river as an international waterway. In 1921 and 1923, final approval of the Danube River Statute was granted by Austria, Germany, Yugoslavia, Bulgaria, Romania, Great Britain, Italy , Belgium, Czechoslovakia, Hungary, and Greece.

The international Danube Commission was thus established as an authoritative institution with wide powers, including its own flag, the right to levy taxes, and diplomatic immunity for its members. It controlled navigation from the town of Ulm to the Black Sea and kept navigational equipment in good repair. During World War II, free international navigation along the course of the river was interrupted by the hostilities, and a consensus concerning the resumption of navigation was not reached until the Danubian Convention of 1948. The new convention provided for the Danubian countries alone to participate in a reconstituted Danube Commission; of those countries, only West Germany did not join the convention.

Question: Which major river has its source at the confluence of the rivers Brigach and Breg in the Black Forest?
Answer: River Danube